linux-kernel - [PATCH 3.16 279/366] tracing: Fix regex_match_front() to not over compare the test string

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Message-ID: <lsq.1539530741.469351082@decadent.org.uk>
Date:   Sun, 14 Oct 2018 16:25:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Subject: [PATCH 3.16 279/366] tracing: Fix regex_match_front() to not over
 compare the test string

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

commit dc432c3d7f9bceb3de6f5b44fb9c657c9810ed6d upstream.

The regex match function regex_match_front() in the tracing filter logic,
was fixed to test just the pattern length from testing the entire test
string. That is, it went from strncmp(str, r->pattern, len) to
strcmp(str, r->pattern, r->len).

The issue is that str is not guaranteed to be nul terminated, and if r->len
is greater than the length of str, it can access more memory than is
allocated.

The solution is to add a simple test if (len < r->len) return 0.

Fixes: 285caad415f45 ("tracing/filters: Fix MATCH_FRONT_ONLY filter matching")
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/trace/trace_events_filter.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -273,6 +273,9 @@ static int regex_match_full(char *str, s

 static int regex_match_front(char *str, struct regex *r, int len)
 {
+	if (len < r->len)
+		return 0;
+
 	if (strncmp(str, r->pattern, r->len) == 0)
 		return 1;
 	return 0;